Jerusalem -LRB- CNN -RRB- -- The websites of the Tel Aviv Stock Exchange and of El Al , the Israeli airline , were brought down Monday morning by an apparent hacking attack .

An internet hacker who calls himself Ox Omar sent an e-mail to the Jerusalem Post Monday in which he claims that together with a hacking group calling themselves `` Nightmare '' that the websites of the Tel Aviv Stock Exchange and that of El Al would be brought down .

Idit Yaaron , the spokeswoman for the Tel Aviv Stock Exchange , told CNN that the main site of the stock exchange where the trading takes place was not harmed and operates on a very high level of Internet security . Trading has continued unaffected , she said . A secondary internet web site was affected for a short period of time .

El Al spokesman , Ran Rahav , released a statement saying , `` El Al is aware that for the past two weeks a cyber war is raging against Israel . The company is closely monitoring the Saudi hacker activity . El Al is taking precautions regarding its website and as a result there may be disruptions in the activity of the website . ''

The `` cyber war '' started at the beginning of the month when a group claiming to be Saudi Arabian hackers posted the credit card information and other identifying data of thousands of Israelis on line , prompting an international investigation .

`` Hi , It 's Ox Omar from the group xp , largest Wahhabi group of Saudi Arabia '' read a statement posted on an Israeli sports web site the group hacked into . `` We are anonymous Saudi Arabian hackers . We decided to release -LRB- the -RRB- first part of our data about Israel . '' Wahhabism is an Islamic religious movement .

The Bank of Israel released a statement last Tuesday saying that , based on information from credit card companies , only around 15,000 credit card numbers were exposed and those credit cards were blocked for use in Internet and phone purchases .

Yoram Hacohen , who heads the Israeli Law , Information and Technology Authority at the Israeli Ministry of Justice , told CNN in a phone interview on Friday that he is more concerned about the private information that was released than the actual credit card numbers ; he fears that the publishing of e-mail addresses , phone numbers and home addresses could lead to identification theft .

Hacohen said that hacking is a criminal act against citizens and the Israeli authorities have begun a criminal investigation , including a computer forensic probe to search for electronic evidence in an attempt to locate the group . The theft of personal information is a criminal act under Israel 's Privacy Protection law .

Hacohen acknowledged that in the digital world , offenders are difficult to track and authorities are asking for international help in the matter .

Israeli Deputy Foreign Minister Danny Ayalon , speaking at a public event , called the Saudi hackers attack `` a breach of sovereignty comparable to a terrorist operation and -LRB- it -RRB- must be treated as such . '' A few days later his own website was targeted in a cyber attack . In a statement on his Facebook page , Ayalon wrote that `` Muslim extremists '' hacked into his website `` to try and prevent me from continuing to do my work on behalf of the State of Israel , especially my online public diplomacy .

Prime Minister Benjamin Netanyahu created a National Cyber Directorate in 2011 , noting the emergence of cyber attacks that could `` potentially paralyze life systems -- electricity , communications , credit cards , water , transportation , traffic lights . ''

He said in December that the new agency -- along with a rocket defense system and a physical fence -- would help protect Israel against its enemies .

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Saudi hackers say in an e-mail they attacked the sites

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Earlier Saudi hackers had exposed thousands of Israeli credit card numbers

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Deputy foreign minister has his website hacked